Semiconductor device

ABSTRACT

The present invention provides a semiconductor device that has reduced a short-channel effect by preventing the effective channel length at the sides of a channel of a transistor from decreasing by forming the length of a gate electrode to be different according to the parts. The semiconductor device according to the present invention includes a semiconductor substrate including active regions where a semiconductor device is to be fabricated and isolation regions for electrically isolating the active regions. A gate electrode is formed to go across the active region. A source and a drain are formed in the active region at both sides of the gate electrode, wherein the length of the gate electrode on the upper surface of the sides of the active region is longer than the length of the gate electrode of the center of the active region.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Korean Patent Application No. 3936/2000, filed on Jan. 27, 2000, the disclosure of which is incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device and, in particular, to a semiconductor device capable of reducing a short-channel effect.

2. Description of the Related Art

FIG. 1 illustrates the structure of a conventional semiconductor device or transistor. As illustrated in the drawing, active regions 101 and inactive regions 102 are formed on a semiconductor substrate 100. A word line 103 having a certain width is formed on an upper surface of the semiconductor device 100. The word line 103 includes a pattern of lines carrying a gate oxide film (not shown). The word line 103 crosses the active region 101 in a vertical direction. The word line 103 divides the active region 101 to form a source 104 and a drain 105. In addition, the intersection of the word line 103 with the active region 101 forms a gate electrode 103 a in an upper part of the active region 101. A channel is formed when a certain voltage is applied to the gate electrode 103 a.

As shown in FIG. 1, Lc is a gate length of the center of the channel, and Le is a gate length of the sides of the channel. In the conventional transistor of FIG. 1, the gate length (Lc) of the center of the channel is the same as the gate length (Le) of the sides of the channel. The conventional transistor having the channel with this type of shape includes a number of disadvantages after implanting impurity ions and annealing the transistor.

FIG. 2 illustrates the conventional transistor after the formation of a lightly doped drain (LDD). Impurity ions are implanted in a portion of the gate electrode 103 a. Annealing the transistor diffuses the implanted impurity ions down to the gate electrode 103 a, as represented by portions 201. As seen in the drawing, diffusion of the impurity ions occurs more extensively at the corners of the channel than at the center of the channel. A transistor formed by this process has an effective length of the channel of the corners (Leffe) that is relatively shorter than an effective length of the channel of the center (Leffc). As a result, a leakage current is increased and a threshold voltage is lowered at the corners of the channel. For these reasons, it is desirable to form a transistor having an effective length of a channel of the corners that is about equal to an effective length of a channel of the center.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a semiconductor device which can reduces a short-channel effect by preventing the effective channel length at the corner of a channel of a transistor from decreasing by forming a gate electrode to have different lengths according to the parts.

The semiconductor device according to the present invention includes a semiconductor substrate including active regions where a semiconductor device is to be fabricated and isolation regions for electrically isolating the active regions. A gate electrode is formed to go across the active region. A source and a drain are formed in the active region at both sides of the gate electrode, wherein the length of the gate electrode on the upper surface of the sides of the active region is longer than the length of the gate electrode of the center of the active region.

BRIEF DESCRIPTION OF THE INVENTION

The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate presently preferred embodiments of the invention, and, together with the general descriptions given above and the detailed descriptions given below, serve to explain features of the invention.

FIG. 1 shows a top view of a conventional semiconductor device;

FIG. 2 shows a top view of the device of FIG. 1 showing a diffusion profile of impurity ions;

FIG. 3 shows a top view of a semiconductor device according to the present invention; and

FIG. 4 shows a top view of the device of FIG. 3 showing a diffusion profile of impurity ions.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, FIG. 3 shows an example of a semiconductor device or transistor according to the present invention. The semiconductor device includes active regions 301 where a transistor is to be fabricated, and isolation regions 302 for electrically isolating the active regions 301, each formed on a semiconductor substrate. A word line 303 is formed in a generally vertical direction across the active region 301. The word line 303 divides the active region 301 to form a source 304 and a drain 305. The intersection of the word line 303 and the active region 301 forms a gate electrode or region 303 a in an upper part of the active region 301.

The gate region 303 a includes a length L1 on an upper surface of the sides of the gate region 303 a of the active region 301, and a length L2 on an upper surface of the center of the gate region 303 a. The length of the sides of the gate region (L1) is greater than the length of the center of the gate region (L2). Thus, as shown in FIG. 3, the gate region 303 a is in the shape of a “dumbbell” or an “hourglass”, wherein the center length L2 is relatively shorter than the side length L1.

FIG. 4 shows a diffusion profile of impurity ions. Impurity ions are diffused down to the gate electrode 303 a, represented by doped region 401. As illustrated in the drawing, although the impurity ions are diffused more extensively at the side of gate electrode 303 a, an effective channel length of the sides of the channel (Leffe′) is about the same as an effective channel length of the center of the channel (Leffc′). Thus, a lightly doped drain (LDD) or a source/drain region having impurity ions diffused more extensively channel can be formed where the effective lengths at the sides and the center of the channel (Leffe′ and Leffc′, respectively) are about the same. As a result, leakage current and threshold voltage decreases caused by longer effective channel lengths at the center than at the sides are eliminated.

While the present invention has been disclosed with reference to certain preferred embodiments, numerous modifications, alterations, and changes to the described embodiments are possible without departing from the sphere and scope of the present invention, as defined in the appended claims. Accordingly, it is intended that the present invention not be limited to the described embodiments, but that it have the full scope defined by the language of the following claims, and equivalents thereof. 

What is claimed is:
 1. A semiconductor device, comprising: a semiconductor substrate including active regions where a semiconductor device is to be fabricated and isolation regions for electrically isolating the active regions; a gate electrode formed to go across the active region, the gate electrode including first and second portions, each having lateral sidewall and center regions; and a source and a drain formed in the active region at both sides of the gate electrode, wherein the length of the first portion of the gate electrode on the upper surface of the sides of the active region is longer than the length of the second portion of the gate electrode of the center of the active region, and the lateral sidewall regions have a first impurity density different than a second impurity density of the center regions.
 2. The device of claim 1, wherein the gate electrode is formed in a dumbbell shape.
 3. A semiconductor device, comprising: a source; a drain; and a gate region having first and second portions each having lateral sidewall and center regions disposed between the source and the drain, the gate region having a first length at a periphery of the source and the drain, and a second length at a center of the source and the drain, wherein the first length is substantially greater than the second length and a first impurity density of the sidewall regions of the first and second portions is different than a second impurity density of the center regions of the first and second portions.
 4. The semiconductor according to claim 3, wherein the gate region comprises an hourglass shape.
 5. A semiconductor device, comprising: a source; a drain; and a gate region having first and second portions separating the source and the drain, the gate region including an edge length at an edge of the source and the drain, and a center length at a center of the source and the drain, wherein the edge length is substantially greater than the center length and the first portion has a first impurity density and the second portion has a second impurity density different than the first impurity density.
 6. The semiconductor according to claim 5, wherein the edge length includes a doped edge length and an undoped edge length, and the center length includes a doped center length and an undoped center length, wherein the doped lengths are adjacent the source and drain.
 7. The semiconductor according to claim 6, wherein the doped edge length is about longer than the doped center length.
 8. The semiconductor according to claim 7, wherein the undoped edge length is about the same size as the undoped center length.
 9. The semiconductor according to claim 7, wherein the undoped edge length is about not less than the undoped center length.
 10. The semiconductor according to claim 6, wherein the doped edge length is about longer than the doped center length, and the undoped edge length is about the same length as the undoped center length.
 11. The device of claim 1, wherein the first impurity density is greater than the second impurity density.
 12. The semiconductor according to claim 3, wherein the first impurity density is greater than the second impurity density.
 13. The semiconductor according to claim 5, wherein the first impurity density is greater than the second impurity density. 